Pump silencing device



F. A. FIRESTONE ET AL 2,155,756

A ril 25, 1939.

' PUMP SILENCING DEVICE Filed April 30, 1937 FIGI Inventors:

MSW

Patented Apr. 25, 1939 UNITED STATES PATENTIQOFFICE 2,155,750 PUMP smmcma DEVICE Floyd A. Firestone, Ernest 1. Abbott, and John D. Kraus, Ann Arbor, Mich.

Application April 30, 1937, Serial No. 140,036

3 Claims. (Cl. 230-145) Our invention relates to the introduction of a pressure relief passage near the exhaust port of a compressor or pumping machine. This passage extends from the exhaust chamber to a nearby point in the cylinder chamber. The function of this passage is to facilitate a gradual, as contras'ted to a sudden, equalization of pressures in the exhaust chamber and cylinder chamber .as

the end of the exhaust strokeis reached.

- Fig. 3 is a side view of the cylinder, in which the outer cylinder end plate I and bearing plate 2 (Fig. 1 and Fig. 2) have been removed exposing the internal cylinder assembly or working cham :ber. Fig. 4 is a view of the outer end plate I.

Similar numerals refer to similar parts in the four views.

The side of the outer cylinder end plate I shown in Fig. 4 is the one which is placed against the cylinder or ca'sing member 3 (Fig. 3), i. e., so that bolt hole 4 in the end plate I is over hole 5 in the cylinder and hole 6 in the end plate over hole I in thecylinder. Circle 8 in Fig. 4 indicates the line of contact of the edge of the cylinder wall 9 with the outer cylinder end.

plate I.

A rotary piston member or roller Ill mounted on an eccentric or crank arm I I has moving contact with the peripheral well of the cylinder chamber sweeping out the cylinder volume once each revolution. The eccentric II turns with the shaft I2 driven by a suitable means not shown. The roller moves in contact with a movable blade or abutment I3 which is held by springs Il against the roller III at all times, dividing the cylinder or working chamber into a high pressure or outlet side, chamber I5, and a low pressure or intake side I6. The blade I3 slides in a slot H in the cylinder 3 which extends back into a member I8 which forms a part of the cylinder assembly. This member I8 also holds the bracket I9 which supports one end of each spring I4. The blade executes a reciprocating motion in synchronism with the rotary motion of the roller and crank. The exhaust or discharge port 20 above the blade permits the passage of gas, air, vapor or liquid into the exhaust or discharge chamber 2|. The intake or inlet port 22 below the blade admits gas to the low pressure side of the cylinder IS. The intake port 22 connects to the intake pipe 23. One end of the cylinder or working chamber is closed by the outer cylinder 5 end plate I and the other by an inner end plate 24. The outer end plate I is held against the cylinder by hearing plate 2. The entire assembly, cylinder, end plates, and bearing plate, is secured by bolts 25 to a suitable frame structure of the compressor not shown. The bearing plate 2 also acts as a bearing for the shaft I2.

The gas compressed in the high pressure side of the cylinder chamber I5 during the motion of the roller In is forced thru the exhaust port 20 15 into the exhaust chamber 2|. From the exhaust chamber the gas passes thru the hole or outlet port 26 in the outer end plate I into a valve chamber 21 in the bearing plate 2 and from there thru outlet tube 23 into a high pressure chamber 20 or reservoir. An exhaust valve 29, held in place by spring 30, covers the outlet port 26. The valve is open only when the pressure in the exhaust chamber is greater than thatin the high pressure reservoir. We define the clearance volume to include the exhaust chamber 2| and to be that region within the high pressure side I5 of the compressor up to the exhaust valve 29 at the time when the volume of this high pressure side is a minimum.

In the ordinary operation of such a pump, as the line of contact 3| of the roller Ill with the cylinder wall 3 approaches the blade I3, i. e., as

the exhaust stroke nears completion, a pressure is built up in the clearance volume which .is greater 35 than the pressure in the reservoir against which the pump operates. As the point of contact 3| of the roller with the cylinder passes the exhaust port 20 the gas under pressure in the clearance volume blows back suddenly into the cylinder where the gas is under low or intake pressure. This sudden change in pressure has been found to produce a click, knock, or clatter in. the operation of the pump at its normal speeds.

Our invention relates to the introduction of a pressure relief groove or passage 32 (Figs. 1, 2, and 4) in the end plate I and facilitates a more gradual equalization of the pressures in the exhaust chamber 2| and the cylinder chamber I6 at the end of the exhaust stroke in the following manner:

When the endplate is assembled against the cylinder 3 the pressure relief groove 32 occupies the position indicated by the dotted lines 32 (Fig. 3) and affords a passage from the clear- 55 groove. By the time the rollers line of contact 3! with the cylinder wall, moving counter-clock.

wise in Fig. 3, has reached the exhaust port 20 and the clearance volume is completely opened to the cylinder, the pressure relief groove has occurs in the operation of the pump. It has been found also that the groove reduces knocking which may occur during starting of the pump.

The length and cross-section of the pressure relief groove or passage, its placement and its points of entrance into the clearance volume and cylinder chamber may vary somewhat in different pumps for best results. Instead of the pressure relief groove being located in the outer end plate I it can be placed in the inner end plate 24, in the cylinder proper at the position indicated by the dotted lines 32 or can be a hole in the cylinder or a depression in the cylinder wall leading from the clearance volume to a point in the cylinder wall. This latter form of construction has some special advantages and might consist merely of a narrow tangential groove milled in the cylinder wall face and leading from the point 20 to the point 35. If this groove is deep at the point 20 and tapers out toward the point 34, the effective passageway for the flow of gas will be smallest at first when the pressure differential is greatest, and will gradually increase as the pressure differential decreases and the.

roller moves. This construction therefore enables one to discharge the clearance volume at a controlled rate. Using a groove 32 in the end plate I to form the passages as shown in the drawing, on a pump of two and one-half inches cylinder diameter, a satisfactory length was three-quarters of an inch and a cross-section of .020" x .020". In what follows, wherever the expressions restricted passage or small depression are used, it is to be understood that the amount of the restriction or the smallness of the depression are to be judged with reference to the function which is to be performed, namely, the equalization of the pressures in the clearance volume and intake volume gradually. It is this gradual pressure equalization, requiring a considerable fraction of the period of the cycle of operation, which permits quiet operation of the pump. The size of passage to best achieve this gradual pressure equalization depends on a number of factors, such as the size of the clearance volume, the speed of operation, the nature of the medium being pumped, etc. While others have used passages of a similar nature for the purpose of permitting the escape of gas pocketed in the cylinder after the closing of a positively operated valve, their passages were large in comparison with the clearance volume so that the equalization of pressure was not gradual but sudden, with consequent production of noise.

The pressure relief groove has a negligible effect on the efliciency of the pump since its opening ll into the cylinder chamber is placed near enough to the exhaust port 20 that the exhaust stroke is essentially complete by the time the opening-l4 is uncovered by the roller 10. The exhaust valve 29 is closed when the pressure relief groove operates. The gas which flows back thru the groove 32 would all blow back in any case an instant later when the exhaust port 20 is uncovered by the roller I 0 if the pressure relief groove were not present.

Our invention may be applied substantially as shown to various sizes of pumps having varions-dimensions and designs of exhaust port, exhaust chamber, valve, and cylinder. The invention' 'canlie'" 'pplied-tdv'acuum pumps as well as to pressure'pumps.

reduced the pressure in the exhaust chamber 2i to a value so close to thatin the low pressure side of the cylinder l6 that no knock'or'click Fla-c a mant g 1. A rotary p comprising a casing member having a fluid working chamber therein, an end plate secured to said casing member and closing said working chamber, said working chamber having fluid inlet and discharge ports, said discharge port leading to a discharge chamber having an outlet port, an outlet valve covering said outlet port, a drive shaft extending within said working chamber, a rotary piston member eccentrically mounted on said drive shaft to have moving contact with the peripheral wall of said working chamber, a moveable abutment sage in said end plate and extending from a point in communication with the pump discharge chamber into communication with a point in the pump working chamber which latter point is within the outlet side of the pump during part of the cycle of motion of the pump piston and within the intake side of the pump during part of said cycle of motion.

2. A rotary pump comprising a casing member having a fluid working chamber therein, an end plate secured to said casing member and closing said working chamber, said working chamber having fluid inlet and discharge ports, said discharge port leading to a discharge chamber having an outlet port, an outlet valve covering said outlet port, a drive shaft extending within said working chamber, a rotary piston member eccentrically mounted on said drive shaft to have moving contact with the peripheral wall of said working chamber, a moveable abutment carried by the peripheral wall of said working chamber at a point between said inlet and outlet ports,

said abutment contacting said piston member and separating said inlet and discharge ports, a restricted depression in the bounding surface of the working chamber and'extending from a point in communication with the pump discharge port to a point which is within the outlet side of the pump during part of the cycle of motion of the pump piston and within the intake side of the pump during part of said cycle of motion.

3. A rotary pump comprising a casing member having a fluid working chamber therein, an end plate secured to said casing member and closing said working chamber, said working chamber having fluid inlet and discharge ports, said discharge port leading to a-discharge chamber having an outlet port, an outlet valve covering said outlet port, a drive shaft extending within said working chamber, a rotary piston member eccentrically mounted on said drive shaft to have moving contact with the-peripheral wall of said working chamber, a moveable abutment carried by the peripheral wall of said working chamber at a. point between said inlet and outlet ports,

1 said abutment contacting said piston member working chamber which latter point is within the outlet side of the pump during part of the cycle of motion of the pump piston and within the intake side of the pump during part of said cycle of motion. FLOYD A. FIRESTONE. ERNEST J. ABBOTT. JOHN D. KRAUS. 

